Magnesium Sulfate (Page 3 of 4)

8.4 Pediatric Use

The safety and effectiveness of Magnesium Sulfate in 5% Dextrose Injection have been established for the prevention of eclampsia in adolescents with preeclampsia and the treatment of seizures and prevention of recurrent seizures in adolescents with eclampsia. Dosing recommendation in pregnant adolescent patients are the same as for pregnant adult patients [see Dosage and Administration (2.2)].

8.6 Renal Impairment

Magnesium is excreted solely by the kidneys. Patients with severe renal impairment (urine output less than 100 mL per 4 hours) are at greater risk for increased magnesium concentrations that may lead to magnesium toxicity [see Warnings and Precautions (5.2) and Clinical Pharmacology (12.3)]. In patients with severe renal impairment, dosage reduction is recommended and the maximum recommended dosage is lower than patients with normal renal function [see Dosage and Administration (2.3)].


Manifestations of magnesium toxicity include a drop in blood pressure, difficulty breathing, and disappearance of the patellar reflex. As serum magnesium rises above 4 mEq per liter, the deep tendon reflexes decrease. As the serum magnesium level approaches 10 mEq per liter, the tendon reflexes disappear and respiratory paralysis may occur [see Warnings and Precautions (5.2)]. Other signs and symptoms of magnesium overdosage include flushing, sweating, hypotension, weakness, hypothermia, circulatory collapse, cardiac and central nervous system depression proceeding to respiratory paralysis, cardiac arrest, and prolongation of PR and QRS intervals. Patients with renal impairment and underlying neuromuscular diseases such as myasthenia gravis may experience magnesium intoxication at lower magnesium concentrations (Magnesium Sulfate in 5% Dextrose Injection is contraindicated in patients with myasthenia gravis).

If patient is experiencing magnesium toxicity, immediately discontinue Magnesium Sulfate in 5% Dextrose Injection. Artificial respiration may be required. Administer an injectable calcium salt to counteract the potential hazards of magnesium toxicity [see Warnings and Precautions (5.2)].

Hypermagnesemia in the newborn (after administration of Magnesium Sulfate in 5% Dextrose Injection to the mother) may require resuscitation and assisted ventilation via endotracheal intubation or intermittent positive pressure ventilation as well as intravenous calcium.


Magnesium Sulfate in 5% Dextrose Injection, USP is a sterile, nonpyrogenic solution of magnesium sulfate heptahydrate and dextrose in water for injection for intravenous use. Each 100 mL contains 1 gram of magnesium sulfate heptahydrate and dextrose, hydrous 5 grams in water for injection [see How Supplied/Storage and Handling (16)]. Magnesium Sulfate in 5% Dextrose Injection, USP may contain sulfuric acid and/or sodium hydroxide for pH adjustment. The pH is 4.5 (3.5 to 6.5).

Magnesium Sulfate, USP heptahydrate is chemically known as sulfuric acid magnesium salt (1:1), heptahydrate and chemically designated MgSO4 ∙ 7H2 O, with a molecular weight of 246.47. It occurs as colorless crystals or white powder freely soluble in water.

Dextrose, USP is chemically designated D-glucose, monohydrate, a hexose sugar freely soluble in water. The molecular formula is C6 H12 O6 ∙ H2 O and the molecular weight is 198.17. It has the following structural formula:

Chemical Structure

Water for Injection, USP is chemically designated H2 O.

Water can permeate from inside the flexible plastic container (polyvinylchloride) into the overwrap [see Dosage and Administration (2.1)] but not in amounts sufficient to affect the solution significantly. Solutions in contact with the plastic container may leach out certain chemical components from the plastic in very small amounts; however, biological testing was supportive of the safety of the plastic container materials. Exposure to temperatures above 25°C (77°F) during transport and storage will lead to minor losses in moisture content. Higher temperatures lead to greater losses. It is unlikely that these minor losses will lead to clinically significant changes within the expiration period.


12.1 Mechanism of Action

Magnesium prevents seizures in patients with preeclampsia and controls seizures in patients with eclampsia by blocking neuromuscular transmission and decreasing the amount of acetylcholine liberated at the end plate by the motor nerve impulse. Magnesium has a depressant effect on the central nervous system [see Drug Interactions (7)]. Magnesium acts peripherally to produce vasodilation.

12.2 Pharmacodynamics

With intravenous administration of magnesium sulfate the onset of anticonvulsant action is immediate and lasts about 30 minutes. The estimated magnesium concentration (above baseline) required to elicit half-maximum effect (EC50 ) on systolic and diastolic blood pressure in pregnant women with preeclampsia that received intravenous magnesium sulfate therapy was reported to be 1.5 and 1.8 mEq per liter (1.9 and 2.2 mg per dL), respectively, in a published study. Effective anticonvulsant serum concentrations range from 2.5 to 7.5 mEq per liter.

Drug Interaction Studies

The following information is based upon published case reports and clinical studies that could not be confirmed by an adequately controlled study, but still warrant consideration given the potential risks involved [see Drug Interactions (7)].

Neuromuscular Blocking Agents:

Potentiation and prolongation of neuromuscular blockade requiring modification of the neuromuscular blocking agent dosage and/or increased reversal agent requirements were reported in preeclamptic women who received magnesium sulfate treatment who underwent subsequent surgery (for example, caesarian section) with anesthesia that included either a depolarizing (d-tubocurarine, succinylcholine) or nondepolarizing neuromuscular blocking agent (vecuronium, rocuronium).

Narcotics and/or Propofol:

Potentiation and prolongation of analgesic and/or sedative effects as well as a reduced requirement for an intravenous narcotic (fentanyl, sufentanil, tramadol), intrathecal narcotic (fentanyl), and/or intravenous propofol was reported in magnesium sulfate treated patients who required surgery or intensive care that also included narcotic and/or propofol therapy.

Dihydropyridine Calcium Channel Blockers:

An exaggerated hypotensive response (blood pressure 80–93/49–60 mm Hg) was reported in preeclamptic women who received oral nifedipine in addition to magnesium sulfate treatment. Blood pressure returned to previous levels within approximately 30 minutes with supportive care.

12.3 Pharmacokinetics


Approximately 1 to 2% of total body magnesium is located in the extracellular fluid space. Magnesium is 30% bound to albumin.


The average half-life and systemic clearance of magnesium sulfate in preeclamptic women is approximately 4 to 5 hours and 4 to 5 liters per hour, respectively.


Magnesium is excreted solely by the kidney at a rate proportional to the serum concentration and glomerular filtration.

Specific Populations

Patients with Renal Impairment:

Plasma magnesium concentrations of 7 to 12.3 mEq per liter (8.6 to 15.1 mg per dL) were reported in preeclamptic women with a urine output less than 100 mL per 4 hours that received 20 grams of magnesium sulfate intravenously over 2 to 8 hours in a published study [see Dosage and Administration (2.3) and Use in Specific Populations (8.6)].


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